Search results

International audience ; This article presents a review of the applications in geosciences of digital elevation model (DEM) time series from satellite stereoscopic imagery for the observation of geometric changes at the Earth's surface. This method dates back to the beginning of the 2000's as a consequence of the multiplication of imaging satellites. We present the evolution of the data availability from the birth of the method for military purpose to its propagation in the civilian sphere. The various methods used for analysing series of digital elevation models are presented, as well as their applications in glaciology, hydrology, volcanology, seismology and geomorphology. Given the constant improvement of the image quality and resolution, the range of applications should continue to grow. ; Cet article présente une revue des applications en géosciences des séries temporelles de modèles numériques d'élévation (MNE) calculés par photogrammétrie spatiale pour l'observation des changements géométriques à la surface terrestre. Les premières utilisations de MNE dans ce contexte émergent au début des années 2000, facilitées par la multiplication des satellites imageurs haute ou moyenne résolution. La disponibilité des images satellite stéréoscopiques est retracée depuis ses débuts militaires jusqu'à sa propagation dans le civil. Les différentes méthodes de traitements de MNE multi-temporels sont présentées ainsi que leur utilisation dans les travaux scientifiques en glaciologie, hydrologie, volcanologie, sismologie, et en géomorphologie. Grâce à l'amélioration constante de la qualité et résolution des images, le spectre des phénomènes observés devrait continuer de s'étendre.

International audience ; This article presents a review of the applications in geosciences of digital elevation model (DEM) time series from satellite stereoscopic imagery for the observation of geometric changes at the Earth's surface. This method dates back to the beginning of the 2000's as a consequence of the multiplication of imaging satellites. We present the evolution of the data availability from the birth of the method for military purpose to its propagation in the civilian sphere. The various methods used for analysing series of digital elevation models are presented, as well as their applications in glaciology, hydrology, volcanology, seismology and geomorphology. Given the constant improvement of the image quality and resolution, the range of applications should continue to grow. ; Cet article présente une revue des applications en géosciences des séries temporelles de modèles numériques d'élévation (MNE) calculés par photogrammétrie spatiale pour l'observation des changements géométriques à la surface terrestre. Les premières utilisations de MNE dans ce contexte émergent au début des années 2000, facilitées par la multiplication des satellites imageurs haute ou moyenne résolution. La disponibilité des images satellite stéréoscopiques est retracée depuis ses débuts militaires jusqu'à sa propagation dans le civil. Les différentes méthodes de traitements de MNE multi-temporels sont présentées ainsi que leur utilisation dans les travaux scientifiques en glaciologie, hydrologie, volcanologie, sismologie, et en géomorphologie. Grâce à l'amélioration constante de la qualité et résolution des images, le spectre des phénomènes observés devrait continuer de s'étendre.

International audience ; This article presents a review of the applications in geosciences of digital elevation model (DEM) time series from satellite stereoscopic imagery for the observation of geometric changes at the Earth's surface. This method dates back to the beginning of the 2000's as a consequence of the multiplication of imaging satellites. We present the evolution of the data availability from the birth of the method for military purpose to its propagation in the civilian sphere. The various methods used for analysing series of digital elevation models are presented, as well as their applications in glaciology, hydrology, volcanology, seismology and geomorphology. Given the constant improvement of the image quality and resolution, the range of applications should continue to grow. ; Cet article présente une revue des applications en géosciences des séries temporelles de modèles numériques d'élévation (MNE) calculés par photogrammétrie spatiale pour l'observation des changements géométriques à la surface terrestre. Les premières utilisations de MNE dans ce contexte émergent au début des années 2000, facilitées par la multiplication des satellites imageurs haute ou moyenne résolution. La disponibilité des images satellite stéréoscopiques est retracée depuis ses débuts militaires jusqu'à sa propagation dans le civil. Les différentes méthodes de traitements de MNE multi-temporels sont présentées ainsi que leur utilisation dans les travaux scientifiques en glaciologie, hydrologie, volcanologie, sismologie, et en géomorphologie. Grâce à l'amélioration constante de la qualité et résolution des images, le spectre des phénomènes observés devrait continuer de s'étendre.

International audience ; This article presents a review of the applications in geosciences of digital elevation model (DEM) time series from satellite stereoscopic imagery for the observation of geometric changes at the Earth's surface. This method dates back to the beginning of the 2000's as a consequence of the multiplication of imaging satellites. We present the evolution of the data availability from the birth of the method for military purpose to its propagation in the civilian sphere. The various methods used for analysing series of digital elevation models are presented, as well as their applications in glaciology, hydrology, volcanology, seismology and geomorphology. Given the constant improvement of the image quality and resolution, the range of applications should continue to grow. ; Cet article présente une revue des applications en géosciences des séries temporelles de modèles numériques d'élévation (MNE) calculés par photogrammétrie spatiale pour l'observation des changements géométriques à la surface terrestre. Les premières utilisations de MNE dans ce contexte émergent au début des années 2000, facilitées par la multiplication des satellites imageurs haute ou moyenne résolution. La disponibilité des images satellite stéréoscopiques est retracée depuis ses débuts militaires jusqu'à sa propagation dans le civil. Les différentes méthodes de traitements de MNE multi-temporels sont présentées ainsi que leur utilisation dans les travaux scientifiques en glaciologie, hydrologie, volcanologie, sismologie, et en géomorphologie. Grâce à l'amélioration constante de la qualité et résolution des images, le spectre des phénomènes observés devrait continuer de s'étendre.

International audience ; This article presents a review of the applications in geosciences of digital elevation model (DEM) time series from satellite stereoscopic imagery for the observation of geometric changes at the Earth's surface. This method dates back to the beginning of the 2000's as a consequence of the multiplication of imaging satellites. We present the evolution of the data availability from the birth of the method for military purpose to its propagation in the civilian sphere. The various methods used for analysing series of digital elevation models are presented, as well as their applications in glaciology, hydrology, volcanology, seismology and geomorphology. Given the constant improvement of the image quality and resolution, the range of applications should continue to grow. ; Cet article présente une revue des applications en géosciences des séries temporelles de modèles numériques d'élévation (MNE) calculés par photogrammétrie spatiale pour l'observation des changements géométriques à la surface terrestre. Les premières utilisations de MNE dans ce contexte émergent au début des années 2000, facilitées par la multiplication des satellites imageurs haute ou moyenne résolution. La disponibilité des images satellite stéréoscopiques est retracée depuis ses débuts militaires jusqu'à sa propagation dans le civil. Les différentes méthodes de traitements de MNE multi-temporels sont présentées ainsi que leur utilisation dans les travaux scientifiques en glaciologie, hydrologie, volcanologie, sismologie, et en géomorphologie. Grâce à l'amélioration constante de la qualité et résolution des images, le spectre des phénomènes observés devrait continuer de s'étendre.

Abstract. The Mediterranean region is characterized by intense
rainfall events giving rise to devastating floods. In Maghreb countries such
as Morocco, there is a strong need for forecasting systems to reduce the
impacts of floods. The development of such a system in the case of ungauged
catchments is complicated, but remote-sensing products could overcome the
lack of in situ measurements. The soil moisture content can strongly
modulate the magnitude of flood events and consequently is a crucial
parameter to take into account for flood modeling. In this study, different
soil moisture products (European Space Agency Climate Change Initiative, ESA-CCI; Soil Moisture and Ocean Salinity, SMOS; Soil Moisture and Ocean Salinity by the Institut National de la Recherche Agronomique and Centre d'Etudes Spatiales de la Biosphère, SMOS-IC; Advanced Scatterometer, ASCAT; and
ERA5 reanalysis) are compared to in situ measurements and one continuous
soil-moisture-accounting (SMA) model for basins located in the High Atlas
Mountains, upstream of the city of Marrakech. The results show that the
SMOS-IC satellite product and the ERA5 reanalysis are best correlated with
observed soil moisture and with the SMA model outputs. The different soil
moisture datasets were also compared to estimate the initial soil moisture
condition for an event-based hydrological model based on the Soil
Conservation Service curve number (SCS-CN). The ASCAT, SMOS-IC, and ERA5
products performed equally well in validation to simulate floods,
outperforming daily in situ soil moisture measurements that may not be
representative of the whole catchment soil moisture conditions. The results
also indicated that the daily time step may not fully represent the
saturation state before a flood event due to the rapid decay of soil
moisture after rainfall in these semiarid environments. Indeed, at the
hourly time step, ERA5 and in situ measurements were found to better
represent the initial soil moisture conditions of the SCS-CN model by
comparison with the daily time step. The results of this work could be used
to implement efficient flood modeling and forecasting systems in semiarid
regions where soil moisture measurements are lacking.

In north-western Tibet (34.0 degrees N, 82.2 degrees E) near lake Aru Co, the entire ablation areas of two glaciers (Aru-1 and Aru-2) suddenly collapsed on 17 July and 21 September 2016. The masses transformed into ice avalanches with volumes of 68 and 83 x 10(6) m(3) and ran out up to 7 km in horizontal distance, killing nine people. The only similar event currently documented is the 130 x 10(6) m(3) Kolka Glacier rock and ice avalanche of 2002 (Caucasus Mountains). Using climatic reanalysis, remote sensing, and three-dimensional thermo-mechanical modelling, we reconstructed the Aru glaciers' thermal regimes, thicknesses, velocities, basal shear stresses, and ice damage prior to the collapse in detail. Thereby, we highlight the potential of using emergence velocities to constrain basal friction in mountain glacier models. We show that the frictional change leading to the Aru collapses occurred in the temperate areas of the polythermal glaciers and is not related to a rapid thawing of cold based ice. The two glaciers experienced a similar stress transfer from predominant basal drag towards predominant lateral shearing in the detachment areas and during the 5-6 years before the collapses. A high-friction patch is found under the Aru-2 glacier tongue, but not under the Aru-1 glacier. This difference led to disparate behaviour of both glaciers, making the development of the instability more visible for the Aru-1 glacier through enhanced crevassing and terminus advance over a longer period. In comparison, these signs were observable only over a few days to weeks (crevasses) or were absent (advance) for the Aru-2 glacier. Field investigations reveal that those two glaciers were underlain by soft, highly erodible, and fine-grained sedimentary lithologies. We propose that the specific bedrock lithology played a key role in the two Tibet and the Caucasus Mountains giant glacier collapses documented to date by producing low bed roughness and large amounts of till, rich in clay and silt with a low friction angle. The twin 2016 Aru collapses would thus have been driven by a failing basal substrate linked to increasing pore water pressure in the subglacial drainage system in response to increases in surface melting and rain during the 5-6 years preceding the collapse dates. ; European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013)/ERC grant [320816]; ESA projects Glaciers_cci [4000109873/14/I-NB]; DUE GlobPermafrost [4000116196/15/IN-B]; French Space Agency (CNES); Programme National de Teledetection Spatiale grant [PNTS-2016-01]; CAS Strategic Priority Research [XDA20000000]; NASA (High Mountain Asia Team) ; Open Access Journal. ; This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.

Abstract. Landslides are a major geohazard that cause thousands of fatalities every year. Despite their importance, identifying unstable slopes and forecasting collapses remains a major challenge. In this study, we use the 7 February 2021 Chamoli rock–ice avalanche as a data-rich example to investigate the potential of remotely sensed datasets for the assessment of slope stability. We investigate imagery over the 3 decades preceding collapse and assess the precursory signs exhibited by this slope prior to the catastrophic collapse. We evaluate monthly slope motion from 2015 to 2021 through feature tracking of high-resolution optical satellite imagery. We then combine these data with a time series of pre- and post-event digital elevation models (DEMs), which we use to evaluate elevation change over the same area. Both datasets show that the 26.9×106 m3 collapse block moved over 10 m horizontally and vertically in the 5 years preceding collapse, with particularly rapid motion occurring in the summers of 2017 and 2018. We propose that the collapse results from a combination of snow loading in a deep headwall crack and permafrost degradation in the heavily jointed bedrock. Despite observing a clear precursory signal, we find that the timing of the Chamoli rock–ice avalanche could likely not have been forecast from satellite data alone. Our results highlight the potential of remotely sensed imagery for assessing landslide hazard in remote areas, but that challenges remain for operational hazard monitoring.